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Guided post-acceleration of laser-driven ions by a miniature modular structure.

Kar S, Ahmed H, Prasad R, Cerchez M, Brauckmann S, Aurand B, Cantono G, Hadjisolomou P, Lewis CL, Macchi A, Nersisyan G, Robinson AP, Schroer AM, Swantusch M, Zepf M, Willi O, Borghesi M - Nat Commun (2016)

Bottom Line: All-optical approaches to particle acceleration are currently attracting a significant research effort internationally.Here we introduce the concept of a versatile, miniature linear accelerating module, which, by employing laser-excited electromagnetic pulses directed along a helical path surrounding the laser-accelerated ion beams, addresses these shortcomings simultaneously.These results open up new opportunities for the development of extremely compact and cost-effective ion accelerators for both established and innovative applications.

View Article: PubMed Central - PubMed

Affiliation: School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK.

ABSTRACT
All-optical approaches to particle acceleration are currently attracting a significant research effort internationally. Although characterized by exceptional transverse and longitudinal emittance, laser-driven ion beams currently have limitations in terms of peak ion energy, bandwidth of the energy spectrum and beam divergence. Here we introduce the concept of a versatile, miniature linear accelerating module, which, by employing laser-excited electromagnetic pulses directed along a helical path surrounding the laser-accelerated ion beams, addresses these shortcomings simultaneously. In a proof-of-principle experiment on a university-scale system, we demonstrate post-acceleration of laser-driven protons from a flat foil at a rate of 0.5 GeV m(-1), already beyond what can be sustained by conventional accelerator technologies, with dynamic beam collimation and energy selection. These results open up new opportunities for the development of extremely compact and cost-effective ion accelerators for both established and innovative applications.

No MeSH data available.


Simulations of focusing and post-acceleration by the helical coil.(a) Reduction in beam divergence (filled blue circles) and the gain in energy (filled red squares) for different input proton energies as obtained from simulations carried out for the case shown in Fig. 3b. (b) Comparison between experimental and simulated proton spectra at the detector plane for the case shown in Fig. 3b. An exponential input spectrum for protons (as shown), similar to the one obtained from the reference flat foil, was used in the simulation. (c–f) Simulated spatial profiles of the proton beam at the detector plane produced by different lengths of the helical coil target shown in the case of Fig. 3b. The black scale bars at the bottom left of the images correspond to 2 mm on the RCF plane. A divergent beam of 4.8 MeV protons was used as input in the simulations, which experience maximum accelerating field according to the graph shown in a. The output beam energy in each case is mentioned on the images. The black-dashed circle represents the projection of the exit ring of the coil on the RCF and the red solid circle shows the internal diameter of the coil.
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f4: Simulations of focusing and post-acceleration by the helical coil.(a) Reduction in beam divergence (filled blue circles) and the gain in energy (filled red squares) for different input proton energies as obtained from simulations carried out for the case shown in Fig. 3b. (b) Comparison between experimental and simulated proton spectra at the detector plane for the case shown in Fig. 3b. An exponential input spectrum for protons (as shown), similar to the one obtained from the reference flat foil, was used in the simulation. (c–f) Simulated spatial profiles of the proton beam at the detector plane produced by different lengths of the helical coil target shown in the case of Fig. 3b. The black scale bars at the bottom left of the images correspond to 2 mm on the RCF plane. A divergent beam of 4.8 MeV protons was used as input in the simulations, which experience maximum accelerating field according to the graph shown in a. The output beam energy in each case is mentioned on the images. The black-dashed circle represents the projection of the exit ring of the coil on the RCF and the red solid circle shows the internal diameter of the coil.

Mentions: Particle-tracing simulations (see Methods for more details) carried out using the target parameters and the measured charge pulse characteristics (amplitude, temporal profile and speed) show that in the case of Fig. 3b the pulse is optimally synchronized for input energy 4–5 MeV (see Fig. 4a). While the radial component of the associated field acts on constraining the divergence of these protons, the longitudinal component of the electric field progressively accelerates the leading part of the synchronized proton bunch at a rate close to 0.5 GeV m−1, as shown in Fig. 4c–f. The analogy with a uniformly charged ring model yields an order of magnitude agreement: the longitudinal field has a peak amplitude , while using Q (total charge in the ring)=30 nC (accounting for the charge spreading over two windings) and R=400 μm. As expected, protons in the trailing part of the synchronized bunch experience deceleration during their travel. The protons which are co-propagating with the central portion of the pulse experience virtually no longitudinal field and their energy is unchanged, while they are focused much more strongly, and have already diverged by the time they reach the RCF detector. The simulated proton spectrum agrees well with the experimental data points as shown in Fig. 4b, while using an input proton spectrum mimicking the experimental data from flat foils. The two peaks in the simulated proton spectrum on either side of 5 MeV are due to the simulated energy gain/loss shown in Fig. 4a. Considering that the 108 protons per MeV at the spectral peak, observed in the experimental data, are produced by the post-acceleration of ∼5 MeV protons, Fig. 3c suggests that gradual focussing of synchronous protons along the coil resulted in an overall collection efficiency of 7%, which is three times better than what would be captured, for an undeflected beam, within the solid angle sustained by the exit ring of the coil.


Guided post-acceleration of laser-driven ions by a miniature modular structure.

Kar S, Ahmed H, Prasad R, Cerchez M, Brauckmann S, Aurand B, Cantono G, Hadjisolomou P, Lewis CL, Macchi A, Nersisyan G, Robinson AP, Schroer AM, Swantusch M, Zepf M, Willi O, Borghesi M - Nat Commun (2016)

Simulations of focusing and post-acceleration by the helical coil.(a) Reduction in beam divergence (filled blue circles) and the gain in energy (filled red squares) for different input proton energies as obtained from simulations carried out for the case shown in Fig. 3b. (b) Comparison between experimental and simulated proton spectra at the detector plane for the case shown in Fig. 3b. An exponential input spectrum for protons (as shown), similar to the one obtained from the reference flat foil, was used in the simulation. (c–f) Simulated spatial profiles of the proton beam at the detector plane produced by different lengths of the helical coil target shown in the case of Fig. 3b. The black scale bars at the bottom left of the images correspond to 2 mm on the RCF plane. A divergent beam of 4.8 MeV protons was used as input in the simulations, which experience maximum accelerating field according to the graph shown in a. The output beam energy in each case is mentioned on the images. The black-dashed circle represents the projection of the exit ring of the coil on the RCF and the red solid circle shows the internal diameter of the coil.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837447&req=5

f4: Simulations of focusing and post-acceleration by the helical coil.(a) Reduction in beam divergence (filled blue circles) and the gain in energy (filled red squares) for different input proton energies as obtained from simulations carried out for the case shown in Fig. 3b. (b) Comparison between experimental and simulated proton spectra at the detector plane for the case shown in Fig. 3b. An exponential input spectrum for protons (as shown), similar to the one obtained from the reference flat foil, was used in the simulation. (c–f) Simulated spatial profiles of the proton beam at the detector plane produced by different lengths of the helical coil target shown in the case of Fig. 3b. The black scale bars at the bottom left of the images correspond to 2 mm on the RCF plane. A divergent beam of 4.8 MeV protons was used as input in the simulations, which experience maximum accelerating field according to the graph shown in a. The output beam energy in each case is mentioned on the images. The black-dashed circle represents the projection of the exit ring of the coil on the RCF and the red solid circle shows the internal diameter of the coil.
Mentions: Particle-tracing simulations (see Methods for more details) carried out using the target parameters and the measured charge pulse characteristics (amplitude, temporal profile and speed) show that in the case of Fig. 3b the pulse is optimally synchronized for input energy 4–5 MeV (see Fig. 4a). While the radial component of the associated field acts on constraining the divergence of these protons, the longitudinal component of the electric field progressively accelerates the leading part of the synchronized proton bunch at a rate close to 0.5 GeV m−1, as shown in Fig. 4c–f. The analogy with a uniformly charged ring model yields an order of magnitude agreement: the longitudinal field has a peak amplitude , while using Q (total charge in the ring)=30 nC (accounting for the charge spreading over two windings) and R=400 μm. As expected, protons in the trailing part of the synchronized bunch experience deceleration during their travel. The protons which are co-propagating with the central portion of the pulse experience virtually no longitudinal field and their energy is unchanged, while they are focused much more strongly, and have already diverged by the time they reach the RCF detector. The simulated proton spectrum agrees well with the experimental data points as shown in Fig. 4b, while using an input proton spectrum mimicking the experimental data from flat foils. The two peaks in the simulated proton spectrum on either side of 5 MeV are due to the simulated energy gain/loss shown in Fig. 4a. Considering that the 108 protons per MeV at the spectral peak, observed in the experimental data, are produced by the post-acceleration of ∼5 MeV protons, Fig. 3c suggests that gradual focussing of synchronous protons along the coil resulted in an overall collection efficiency of 7%, which is three times better than what would be captured, for an undeflected beam, within the solid angle sustained by the exit ring of the coil.

Bottom Line: All-optical approaches to particle acceleration are currently attracting a significant research effort internationally.Here we introduce the concept of a versatile, miniature linear accelerating module, which, by employing laser-excited electromagnetic pulses directed along a helical path surrounding the laser-accelerated ion beams, addresses these shortcomings simultaneously.These results open up new opportunities for the development of extremely compact and cost-effective ion accelerators for both established and innovative applications.

View Article: PubMed Central - PubMed

Affiliation: School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK.

ABSTRACT
All-optical approaches to particle acceleration are currently attracting a significant research effort internationally. Although characterized by exceptional transverse and longitudinal emittance, laser-driven ion beams currently have limitations in terms of peak ion energy, bandwidth of the energy spectrum and beam divergence. Here we introduce the concept of a versatile, miniature linear accelerating module, which, by employing laser-excited electromagnetic pulses directed along a helical path surrounding the laser-accelerated ion beams, addresses these shortcomings simultaneously. In a proof-of-principle experiment on a university-scale system, we demonstrate post-acceleration of laser-driven protons from a flat foil at a rate of 0.5 GeV m(-1), already beyond what can be sustained by conventional accelerator technologies, with dynamic beam collimation and energy selection. These results open up new opportunities for the development of extremely compact and cost-effective ion accelerators for both established and innovative applications.

No MeSH data available.